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S. Nicholls, W. Shaw, and T. Hauf

Abstract

During the Joint Air-Sea Interaction (JASIN) experiment over the North Atlantic, three aircraft equipped to measure turbulent fluctuations of wind, temperature and humidity flew together in close formation, in order to compare results. These aircraft were the MRF C130, the NCAR Electra and the DFVLR Falcon. Most runs were made in the atmospheric boundary layer. This paper presents the results of this intercomparison exercise. Results are presented in terms of comparisons between variances and covariances which are further investigated by comparing spectra and co-spectra.

Overall, very good agreement is found between the C130 and the Electra, although small differences can be detected. However, these are negligible compared to the scatter usually observed when making measurements in the turbulent atmospheric boundary layer. The Falcon, at an earlier stage of development, also shows reasonable agreement although the amount of available data was much more limited.

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A. Tafferner, T. Hauf, C. Leifeld, T. Hafner, H. Leykauf, and U. Voigt

Abstract

This paper describes the design of the Advanced Diagnosis and Warning System for Aircraft Icing Environments (ADWICE) and presents results for two different icing weather situations with typical icing conditions. ADWICE has been in development since 1998 through the joint cooperation of the Institute for Atmospheric Physics at the German Aerospace Center (DLR), the German Weather Service (DWD), and the Institute for Meteorology and Climatology of the University of Hannover (IMUK). ADWICE uses information from different data sources in order to identify atmospheric environments that are potentially hazardous for aircraft icing. Forecast data from the operational Local Model (LM) of the DWD, with a horizontal grid spacing of 7 km covering the domain of central Europe, are combined with radar data and routine weather observations from the surface station network for this purpose. Algorithms developed at the National Center for Atmospheric Research (NCAR) that take into account different weather scenarios use the LM forecast fields of temperature, humidity, and pressure to provide first-guess icing information at LM grid points. This first-guess field is then subjected to a scenario correction in which a consistency check is performed through the combined use of the radar data and present weather reports. A final correction of the icing volume is achieved through surface observations of cloudiness and ceiling. For all diagnosed icing points the intensity of icing is derived from a formula that provides an adiabatic estimate of cloud liquid water from water vapor saturation mixing ratio at cloud base and forecast mixing ratios from the LM. Results are presented for a typical case of freezing rain and another one in which pilot reports (PIREPs) of icing are available for comparison. These PIREPS have been collected together with other relevant meteorological data during a testing phase from January to May 2001 in which ADWICE has been run in an operational environment at the DWD. Although ADWICE produces plausible icing fields, uncertainty remains with regard to providing an estimate of the icing intensity at a particular flight level. Taking cloud liquid water as forecast by the LM model directly as a measure of icing intensity instead of the estimate provided by the formula, however, produces poor results, as the comparison with PIREPs indicates.

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T. Hauf, U. Finke, J. Neisser, G. Bull, and J-G. Stangenberg

Abstract

In 1992, a surface-based, mesoscale microbarograph array with four pressure sensors was installed near the Hohenpeißenberg, southern Germany, and has since been in continuous operation. In this paper, a description of the sensors, the network, and the data evaluation is given. The sensors are based on conventional microphone techniques, where the pressure difference between the ambient air and an internal reservoir is measured. The latter is connected with the former by an adjustable needle valve. Pressure fluctuations are resolved with an amplitude resolution of 3 µb and between periods of 2 s and 30 min. Sensors are calibrated by lifting over a given height. Time constants are determined with a pressure-pulse technique and are on the order of 300 s. Data are sampled at 1 Hz and are transmitted on-line to a central data processing unit. Each sensor is installed at the bottom of a 1.50-m-high container, which is mounted flush with the ground. The sensor is thermally insulated and protected such that the air exchange between the sensor and the atmosphere is kept to a minimum. The average sensor separation is 1 km. A wavelet technique is applied to the data from each sensor to isolate the gravity wave events from background fluctuations. It is a general finding that gravity waves are found in wave packets with a maximum of four to five wavelengths only. Wave events are clearly recognizable by their sinusoidal shape. Furthermore, frontal passages, positive and negative solitary waves, and turbulent wind situations can be identified from the pressure signals. Most of the time, background signals are characterized by well-correlated pressure fluctuations of several-microbar amplitude. However, they have irregular shape probably due to the existence of drifting density inhomogeneities.

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P. F. Meischner, M. Hagen, T. Hauf, D. Heimann, H. Höller, U. Schumann, W. Jaeschke, W. Mauser, and H. R. Pruppacher

CLEOPATRA (Cloud Experiment Oberpfaffenhofen and Transports) is described. This field program was performed in southern Germany 50 km north of the Alpine foothills, an area of known enhanced thunderstorm activity. The general goal is to quantify elements of the hydrological cycle on a regional scale in dependence upon precipitation events and the vegetation state. Embedded goals are to describe the mechanisms that force organizations of deep convective systems, to compare theories and observations of atmospheric depositions, and to test and compare observational methods from ground, aircraft, and space. The observational setup, including 10 research aircraft, four radar systems, and different ground-based networks, was operational from 11 May until 31 July 1992 to cover an essential period of the growing season.

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